1. Field of the Invention
The present invention relates to a communication method and a communication apparatus which are applied to the case where data communication is conducted between devices connected by a bus line of, for example, the IEEE 1394 scheme.
2. Description of the Related Art
AV devices capable of mutually transmitting information via a network using a serial data bus of the IEEE 1394 scheme have been developed. When conducting data transmission via this bus, there are prepared an isochronous transfer mode to be used when video data and audio data of a comparatively large capacity are subject to real time transmission, and an asynchronous transfer mode to be used when still images, text data, control commands and so on are transmitted certainly. A dedicated band is used for transmission every mode.
FIG. 18 is a diagram showing an example of connection using a bus of the IEEE 1394 scheme. It is now assumed that a source device “a” which is a device for sending out data, a target device “b” which is a device for receiving data sent out from the source device “a”, and a controller “c” for controlling data transmission between the devices “a” and “b” are connected to a bus “d” of the IEEE 1394 scheme. Assuming at this time that video data is transmitted between the devices “a” and “b” under the control of the controller c, the controller c secures an isochronous transfer channel on the bus “d”, establishes connection between the devices “a” and “b”, and starts transmission from the source “a” to the target device “b”.
In the case where data transmission is thus conducted between the source device “a” and the target device “b”, a transmission scheme of control commands called AV/C command transaction set which can be applied to, for example, AV devices can be applied. Details of the AV/C command transaction set are opened to the public.
Considering data transmission of video data and audio data from the source device to the target device, selection of data which can be inputted to an input device can be conducted freely, if input selection can be conducted on the target device side. Therefore, the present inventors proposed earlier processing of establishing a connection between the target device and the source device and securing a transmission line on the bus (Japanese Patent Application 11-328764).